1. Field of the Invention
The present invention relates to a radio communication system and a channel allocating method in an FDMA (Frequency Division Multiple Access) system. More specifically, the present invention is directed to a radio communication system including a radio signal transmitter and a receiver, and a channel allocating method in the FDMA system in which an FSK (Frequency Shift Keying) modulation is employed.
2. Description of the Related Art
As a multiple access system where a plurality of users perform radio communications at the same time in the same field, the FDMA (Frequency Division Multiple Access) system and the TDMA (Time Division Multiple Access) system are frequently used. Among these systems, the FDMA system is such a system that a radio frequency band assigned to the system is subdivided into a plurality of channels, and radio channels of the respective users are set to radio frequencies different from each other with respect to each of the users. A predetermined frequency interval is provided between the multiplexed channels, so that no interference occurs between the channels. To increase a total number of channels available for multiplexing in an assigned frequency band, it is required to employ such a modulation system capable of reducing an occupied frequency bandwidth per channel as narrow as possible.
The FSK (Frequency Shift Keying) modulation is such a modulation system for varying a frequency of a modulating carrier wave in accordance with a content of data to be transmitted. An occupied frequency bandwidth of an FSK-modulated signal is determined based on a difference between a maximum frequency of a modulating carrier wave and a minimum frequency thereof, namely a magnitude of a maximum frequency shift. The larger the maximum frequency shift becomes, the more the interference between the carrier waves can be suppressed. As a result, the quality of speech communication can be improved.
However, there is a problem that when the maximum frequency shift is excessively increased, since the occupied frequency bandwidth of the modulated signal is widened, a total number of channels to be multiplexed is reduced. In particular, as shown in FIG. 12, when the maximum frequency shift is increased, the bandwidth per 1 channel is increased, so that the number of dividing frequencies to be accommodated in the assigned radio frequency band is reduced, and the multiplexing degrade is decreased.
As a consequence, according to the present invention, a channel allocating method with a high frequency utilizing efficiency is provided in which in the FDMA system, while a maximum frequency shift by the FSK modulation is set to a large value, and also a maximum frequency shift by the OOK (ON/OFF Keying) modulation is set to a large value, a carrier wave frequency of another channel is allocated between carrier wave frequencies of a certain channel.
The present invention is featured by such a channel allocating method used to a frequency division multiple access (FDMA) system by an FSK (Frequency Shift Keying) modulation, wherein: while a maximum frequency shift in the FSK modulation is increased, more than one carrier wave frequencies of other channels are allocated between carrier wave frequencies of a certain channel. Also, the present invention is applied for an OOK (ON/OFF Keying) modulation by similar configuration.
Also, the present invention is featured by such a transmitter apparatus used to a frequency division multiple access (FDMA) system by an FSK (Frequency Shift Keying) modulation, wherein: while a maximum frequency shift in the FSK modulation is increased, more than one carrier wave frequencies of other channels are allocated between carrier wave frequencies of a certain channel. Also, the present invention is applied for an OOK (ON/OFF Keying) modulation by similar configuration.
Also, the present invention is featured by such a receiver apparatus used to a frequency division multiple access (FDMA) system by an FSK (Frequency Shift Keying) modulation, wherein: while a maximum frequency shift in the FSK modulation is increased, a reception signal is received in which more than one carrier wave frequencies of other channels are allocated between carrier wave frequencies of a certain channel. Also, the present invention is applied for an OOK (ON/OFF Keying) modulation by similar configuration.
Further, the present invention is featured by such a channel allocating method used to a frequency division multiple access (FDMA) system by an FSK (Frequency Shift Keying) modulation, wherein: while a maximum frequency shift in the FSK modulation is increased, more than one carrier wave frequencies of other channels are allocated between carrier wave frequencies of a certain channel, and also an interval of the channels is determined by a magnitude of a maximum Doppler frequency. The present invention is also applied for an OOK (ON/OFF Keying) modulation by similar configuration.